The present invention relates generally to pipette devices for drawing and subsequently ejecting a predetermined volume of liquid.
Pipettes are commonly used in chemical, biological and medical research laboratories to draw and dispense accurate quantities of liquid samples. Such pipettes normally comprise hollow glass tubes secured to a suction device or pipettor at one end for drawing a predetermined volume of liquid through the opposite end of the tube and subsequently ejecting the drawn liquid into another vessel for analysis or other treatment. The pipettor or suction device generally comprises a simple pumping device such as a piston or plunger and cylinder arrangement, a simple elastic bulb, a bellows, or other suction device. The pipette is normally cleaned and sterilized or discarded after each use. In medical applications the pipette will normally be discarded to prevent any possibility of contamination or infection.
One major problem with such liquid sampling arrangements is that the pipettor or suction device itself may become contaminated by a liquid sample, resulting in potential hazards to operators as well as cross-over contamination in subsequently drawn samples. One major cause of such contamination is the so-called aerosol effect, in which some of the liquid sample is vaporized and forms droplets which are drawn upwardly with the air as it is drawn out of the pipette by the suction device. Such contamination can also occur if the operator holds the pipette wrongly while drawing or transporting the sample, for example at an angle rather than vertically, if the pipette is jarred or moved too quickly, so that the liquid flows to the pipettor end of the tube, or if the liquid foams or bubbles up the tube.
Previous attempts have been made to alleviate such problems by inserting a physical barrier into the pipette. However, the barrier must necessarily allow gas flow in order to draw and subsequently dispense the liquid sample, and thus does not completely eliminate any risk of contamination. Such barriers are normally of cotton or similar material, which will not completely block passage of aerosol droplets. Additionally, if liquid actually contacts such a barrier, it will be drawn along the barrier by a wicking effect to the upper side, where there is nothing preventing it from contacting the suction device. Thus, there is no guarantee that existing barriers will completely block aerosol droplets, and even small amounts of such droplets give rise to contamination and potential hazards to personnel where infectious materials are concerned. Also, even contact with the barrier itself may give rise to contamination of the drawn sample by the barrier material, and also gives rise to inaccuracies in the amount of liquid dispensed.